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Wednesday, 4 February 2015

An unCommon Gull

Unless you are the most fanatical of birders, a flock of Common Gulls feeding in a field in winter might just about be worth a look, at best for maybe a Ring-billed Gull. This bird, seen yesterday by D. Farrar in a field near the Cashen Estuary, seems to want to give us a shake and make us think again about what might be possible in the murky and difficult world of gull identification.

So, a field full of Common and Herring Gulls, and one adult Common Gull jumps out from the posse. It has a mantle a good shade or two darker than others nearby, close even to our local graellsii Lesser Black-backed Gulls. On closer examination, it also seems to have a pale eye.

(You can click on the images for a closer view)

Common Gull showing dark mantle and hint of a pale eye? (All photos: Davey Farar).

Other subtle features include a slightly longer primary projection and just the faintest of smudges toward the end a longish bill.

The same gull in flight.

And another, in flight (top bird).

A close up of the bill showing just a faint gonys spot.

Comparison with four adult Common Gulls (left) and the much darker individual on right.

So, what could it be? There is a North American version of Common Gull, now often referred to as 'Short-billed Gull' (and just to muddy the waters a little, was formerly called 'Mew Gull') but as the name suggests, the N. American form has a short bill - unlike this one. It is also predominantly a W coast species, breeding in Alaska and wintering S along the W coast of America.

However, there are also two 'eastern' races of Common Gull which show some or all of the features of the above bird. The nearest to us is the subspecies heinii which nests from roughly Moscow, E across Russia to central Siberia, but which winters largely in SE Europe. The other race is camtschatchensis (or Kamtschatschensis) - sometimes called 'Kamchatka Gull' - which breeds in NE Siberia and winters in Japan and E China.

Our own subspecies canus interbreeds with heinii where they overlap in Russia, but camtschatchensis apparently does not, or rarely does, which has prompted proposals that 'Kamchatka Gull' should be split. As to this bird in north Kerry? The jury is out. Better flight shots would be needed, but it does seem to be of one of the two 'eastern races'.

There's more on these races on the Birding Frontiers website HERE and an account of a probable Kamchatka Gull in Newfoundland HERE.

Davey sarched high and low for this bird today, but to no avail. There was another 'eastern Common Gull' seen by David O'Connor at Black Rock in 2013 - we'll post a link/images if we can find out more.

Time to take note of any unusual Common Gulls! Surely Kerry is the most likely spot in Europe to turn up a North American 'Short-billed Gull', and there are also 'Russian Common Gulls' and even 'Kamchatka Gulls' to look out for too. Any of these are possible. If Slaty-backed Gull can reach Ireland twice...